Magnetic metal alloys such as permalloy are commonly used as one of the materials for forming magnetic head assemblies used in computer data storage devices. It is known in the art that the magnetic surfaces of magnetic head assemblies are attacked by moisture and chemicals causing corrosion, which reduces the reliability and accuracy of the head, and can lead to total disk drive failure.
Permalloy is a magnetic nickel-iron alloy which has excellent magnetic properties, but which is subject to corrosion. In particular, water, chlorides and sulfides are known to corrode permalloy. Other magnetic alloys are also susceptible to corrosion. Corrosion commonly occurs during the slider fabrication process on the wafer, which involves much water processing.
Magnetic head assemblies typically include a plurality of exposed magnetic surfaces, such as pole tips at or on the air bearing surface of the “flying head” assembly, for example. The air bearing surfaces for purposes of this disclosure are the surfaces of the magnetic head which contact the magnetic recording media when the magnetic recording media is not in motion. Frictional contact between the magnetic portions of the air bearing surfaces generated during starting and stopping prevents further corrosion.
Although it is known in the art generally that the air bearing surface of a magnetic head can be coated with a layer of anticorrosive material, this layer is not added until after slider fabrication and therefore does not prevent corrosion that occurs between the end of the wafer process and the placing of the layer of anticorrosive material on the head.
One prior art method of preventing corrosion during slider fabrication is the placement of a corrodible anode in the head assembly. The corrodible anode is constructed of a material having an ionization tendency larger than that of the magnetic material, and therefore will sacrificially corrode in place of the material to be protected. The material corrodes instead of protected material by providing a potential to the protected material.
For example, Japanese patent JP 1102710A, Apr. 20, 1989 to Goto Hirochi et al. embeds a thin film corrodible anode in the head structure. The corrodible anode is in contact with magnetic thin films.
However, in prior art methods using corrodible anodes, the corrodible anode remains in the head after processing. As the anode corrodes, it creates corrosion products that remain in the head and which end up in the finished disk drive. The head can run into this debris, resulting in errors.
Another prior art method suggests use of a power supply to provide corrosion protection. However, the user of a power supply is not possible given the grounding requirements for other structures in the disk drive.
The above-mentioned prior art methods fail to disclose a method of protecting the magnetic surfaces of a magnetic head during the slider fabrication process for magnetic recording head assemblies. A corrodible anode which does not remain in the head structure after manufacture, significantly reduces corrosion, does not distort the signal generated by the magnetic recording head, and does not increase the potential for catastrophic hard disk failure would therefore be very desirable.